1. Field of the Invention
The present invention relates to an image forming apparatus provided with a sheet processing device for processing sheets, such as recording sheets, discharged from the image forming apparatus, such as a copying machine, a printer, and a facsimile, especially from a main body of the apparatus in sequence, and selectively carrying out processing, such as punching or stapling, on the sheets.
2. Description of the Related Art
Hitherto, in an image forming apparatus for forming an image on the surfaces of sheets of, for example, a copying machine, there is provided a sheet processing device (finisher) for aligning the discharged sheets in sequence into a plurality of sets, and for carrying out processing such as punching and stapling on the sheets.
The sheet processing device is advantageous because the handling property of the sheets is significantly improved, and thus it has become widely used in recent years.
However, the image forming apparatus having an integral sheet processing device as described above has a problem in that even when the user wants to print on a single sheet, or wants to obtain sheets which do not need sheet processing such as stapling, electric power for initializing each sheet processing unit or for transporting the sheets to a sheet discharge tray located downstream of the sheet processing unit is inevitably consumed even when the sheet processing operation is not carried out.
According to U.S. Pat. No. 6,371,471, there is shown a technology in which power is supplied to an insert sheet feeder only when the user sets the apparatus to deliver the inserted sheet on a control panel. However, the system disclosed in U.S. Pat. No. 6,371,471 is constructed in such a manner that a finisher controller turns ON/OFF the power to a plurality of sheet processing units including the insert sheet feeder, but not the power to the finisher, that is, the sheet processing device itself. Therefore, even when the sheet is discharged onto the discharge tray provided on the image forming apparatus, in other words, even when the sheet is not discharged to the sheet processing device, the system supplies electric power to the sheet processing device itself and carries out an initializing operation for moving movable portions in the sheet processing device to their home positions when power supply is started. Consequently, there remain problems of standby power requirement of the sheet processing device and of operating noise generated when the sheet processing device performs the initializing operation in the case where the sheet is not discharged to the sheet processing device.